<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <select id="sel" onchange="adds()">
		<option value="">请选择前往的网站</option>
		<option value="http://www.baidu.com">百度</option>
		<option value="http://www.163.com">网易</option>
		<option value="http://www.taobao.com">淘宝</option>
	</select>
</body>
<script type="text/javascript">
	function adds(){
		var url = document.getElementById('sel').value;
		console.log(url);
		location.href=url
	}
</script>
</html>